Project Summary/Abstract HIV dual infection (infection of an individual by two different viral strains from different source partners) is an increasingly reported phenomenon in the HIV literature, with consequences for both vaccine design and for the individual, since it has been associated with increased viral load, faster decline in CD4 T-cell count, and a shorter time to AIDS diagnosis. Given that HIV dual infection is associated with these markers of disease progression and immunosuppression, it is also likely that it enhances end organ damage. An important organ system that is commonly damaged during HIV infection is the central nervous system (CNS). In fact, HIV- associated neurocognitive disorder (HAND) continues to be a debilitating disorder affecting the aging HIV patient population, even those who receive highly active antiretroviral therapy (ART). Despite this, the impact of HIV dual infection on neurocognitive functioning remains largely unknown. This proposal builds upon access to the large, well-characterized CNS HIV Anti-Retroviral Therapy Effects Research (CHARTER) cohort to identify cases of HIV dual infection in the blood and CNS. The main objective will be to determine how HIV dual infection is related to neurocognitive impairment among HIV-infected individuals that are receiving ART. Longitudinal samples of peripheral blood mononuclear cells (PBMC) and cerebrospinal fluid (CSF) will be collected from CHARTER participants who were receiving ART. CHARTER participants undergo a comprehensive battery of neuropsychological tests adjusted for demographics to screen for the presence of HAND. Next generation sequencing (NGS) will be performed on four coding regions (env C2-V3, gag p24, pol RT, and pol PR) amplified from PBMC- and CSF-derived HIV DNA populations. Bioinformatics and phylogenetic analysis will be utilized to identify individuals with HIV dual infection and estimate the prevalence of dual infection. Additionally, NGS of full-length HIV will be performed on PBMC samples from individuals identified with dual infection to assess for viral recombination and evolution across the length of the entire HIV genome. Finally, linear regressions and nonparametric testing will be used to examine if a statistically significant difference in HAND exists between the HIV dual infected and monoinfected groups, and to determine virologic correlates of HAND that may be linked to enhanced viral neuroadaptation during dual infection. Using next generation sequencing technology, the work proposed is expected to identify cases of dual infection in both normal and neurocognitively impaired HIV-infected participants that are receiving ART, and thus provide a better understanding of the relationship between HIV dual infection and HAND. Such results would have an important impact, because a deeper understanding of the virologic correlates of HAND is essential and likely to provide new targets for intervention to prevent end organ damage during natural infection.